Computational Design of High-Affinity Blockers for Sodium Channel Na1.2 from μ-Conotoxin KIIIA.

The voltage-gated sodium channel subtype 1.2 (Na1.2) is instrumental in the initiation of action potentials in the nervous system, making it a natural drug target for neurological diseases. Therefore, there is much pharmacological interest in finding blockers of Na1.2 and improving their affinity and selectivity properties. An extensive family of peptide toxins from cone snails (conotoxins) block Na channels, thus they provide natural templates for the design of drugs targeting Na channels. Unfortunately, progress was hampered due to the absence of any Na structures. The recent determination of cryo-EM structures for Na channels has finally broken this impasse. Here, we use the Na1.2 structure in complex with μ-conotoxin KIIIA (KIIIA) in computational studies with the aim of improving KIIIA's affinity and blocking capacity for Na1.2. Only three KIIIA amino acid residues are available for mutation (S5, S6, and S13). After performing molecular modeling and simulations on Na1.2-KIIIA complex, we have identified the S5R, S6D, and S13K mutations as the most promising for additional contacts. We estimate these contacts to boost the affinity of KIIIA for Na1.2 from nanomole to picomole domain. Moreover, the KIIIA[S5R, S6D, S13K] analogue makes contacts with all four channel domains, thus enabling the complete blocking of the channel (KIIIA partially blocks as it has contacts with three domains). The proposed KIIIA analogue, once confirmed experimentally, may lead to novel anti-epileptic drugs.